Model aircrafts are becoming increasingly more complicated and advanced as new electronics and new materials become available. The builder of model aircrafts constantly attempts to improve his model, to make it look like and fly approximately like large, manned airplane. The model aircrafts may be built larger than e.g. a scale of 1:3, and equipped with large gasoline engines of more than e.g. 150 cm3. The engines are either two-stroke or four-stroke, with one or more cylinders. The engines may also be of the turbine type. Since a model aircraft is usually smaller than a manned aircraft, smaller engines are used. In order for a small engine to be able to yield the desired effect, it must work at a high speed as compared with a large engine. This means that the model engine practically has to use a relatively small propeller, as compared with the true scale. If a proper scale model would be used, the model engine would not manage the desired effect. This is because the diameter of the scale propeller together with the propeller""s angle of attack will be too large a strain on the model engine.
An engine yields most effect only at one certain speed and in order to make it possible to build a model aircraft with a scale true propeller and a propeller that may be adjusted to the performance of the engine, it is necessary to use a propeller with a variable angle of attack.
U.S. Pat. Nos. 5,209,640 and 5,299,911 describe a hydraulically operated, electronically controlled, propeller pitch angel controller intended for use in aircrafts. These solutions use complicated sensors transmitting signals to the microprocessor in a microcomputer. U.S. Pat. No. 5,299,911 uses three sensors informing about the engine speed, the carburettor position and the carburettor""s intake pressure. U.S. Pat. No. 5,209,640 has sensors informing about the flying speed, atmospheric pressure, atmospheric temperature, engine speed and the carburettor position.
The U.S. Pat. Nos. 5,209,640 and 5,299,911 describe a microcomputer receiving signals from the sensors to control a hydraulic transmission device, allowing the propeller""s angle of attack to be adjusted. An external pump run by the propulsion engine of the aircraft drives the hydraulic device. Other, not cited, solutions use the propulsion engine""s oil pressure to directly adjust the attack angle of the propeller. The latter is a completely mechanical solution, not using electronic control. It is reasonable to assume that such solutions include heavy and large equipment, making the use in model aircrafts unsuitable. Thus, it may be understood that the above-mentioned solutions are intended for use in manned aircrafts. It would also be problematic and expensive to scale such equipment down for practical use in model aircrafts.
The U.S. Pat. Nos. 5,209,640 and 5,299,911 use 5 and 3 sensors, respectively, to provide the input signals for control of the propeller""s angle of attack. This is more than practically necessary to control the propeller""s angle of attack in a model aircraft. The solutions in the U.S. Pat. Nos. 5,209,640 and 5,299,911 thus represent additional weight and also complicate the control of the angle of attack through more parameters. The present invention comprise only one propeller speed sensor, signalling to one or more micro controllers, and power to the adjustment of the propeller""s angle of attack is provided by an electric servomotor, providing low weight and size. Thus, the present invention represents a solution suitable for use in model aircrafts.
There is a large selection of model aircraft engines for use in various types of model aircrafts. It is also desirable that the engine at all times operates as close to the maximum efficiency as possible. There is thus a need for setting the right working speed and regulation response before the flying takes place. The present invention allows this, through a suitable interface between the model aircraft and the pilot of the model aircraft. This interface may e.g. be a keypad to set the desired speed of the engine and the system""s regulation response, and a display for reading. The U.S. Pat. Nos. 5,209,640 and 5,299,911 mention no equivalent solution.
In other, not cited, solutions, the speed may be adjusted during the flying of manned aircrafts and stationary, manned aircrafts. The regulation response may, however, not be adjusted by the pilot, neither for stationary aircrafts nor during the flying.
The present invention concerns an electronic propeller controller for use in model aircrafts. The engine""s carburettor position is primarily controlled by the operator, while the propeller""s angle of attack is controlled by the propeller controller. There is, however, a possibility for automatic adjustment of the carburettor position of the control unit, although the operator will primarily do this manually before or during the flight.
The speed of the aircraft is given by the propeller""s propulsive force and the aircraft""s aerodynamic characteristics. The propeller""s propulsive force will be adjusted as a consequence of the increase or decrease in the carburettor position. This implies that the propeller""s angle of attack is automatically increased or decreased to adjust the pre-set engine speed.
With model aircrafts are understood radio-controlled or self-monitored, unmanned, not full-scale aircrafts.
One objective of the present invention is to obtain a constant speed propeller controller for use in model aircrafts, allowing the use of a full-scale propeller and that the model engine at the same time may operate with maximum efficiency, independent of the speed of the aircraft.
Another objective of the present invention is to obtain a constant speed propeller controller of such a size and weight that it is practically usable in a model aircraft.
A further objective of the present invention is to obtain a constant speed propeller controller with a considerably more reasonable price than the technique mentioned.